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PEABODY MUSEUM OF NATURAL HISTORY
YALE UNIVERSITY
NEW HAVEN, CONNECTICUT, U.S.A.
Number 110 September 14, 1967
REVISION OF SYNCYCLONEMA (UPPER CRETACEOUS)
AND COMPARISON WITH OTHER SMALL
PECTINID BIVALVES AND ENTOLIUM
IAN G. SPEDEN
NEW ZEALAND GEOLOGICAL SURVEY
Lower Hutt, NEw ZEALAND
ABSTRACT
New descriptions and figures are given for Pecten rigida Hall
& Meek (= Pecten halli Gabb), the type species of Syncyclonema
Meek, and for the type species of genera to which Syncyclonema
is often compared: Entolium Meek, Eburneopecten Conrad, Pec-
tinella Verrill, Hyalopecten Verrill, Camptonectes Agassiz, Micro-
nectes Ichikawa & Maeda, Pseudamussium Morch, and ‘“Pseuda-
mussium” H. & A. Adams. Syncyclonema is shown to be a valid
genus. A lectotype is designated for Syncyclonema halli, and on
the basis of its chlamyiid shape, deep byssal notch, and hinge
morphology Syncyclonema is placed in the family Pectinidae.
These characters invalidate synonymy of Syncyclonema_ with
Entolium and its assignment to the family Entoliidae Korobkov.
i)
Postilla YALE PEABODY MUSEUM No. 110
INTRODUCTION
Hall & Meek’s (1856, p. 381, pl. 1, figs. 4a-c) original
description of Pecten rigida, the type species of Syncyclonema
Meek (1864a), was brief and the accompanying figures rather
indefinite. Consequently, the systematic position of Syncyclonema
and its relationships to other genera have been confused and
controversial. Staesche (1925, p. 90) considered Syncyclonema a
distinct genus and a smooth chlamyiid with a very weak byssal
notch. Verrill (1897, p. 62) hesitantly accepted Syncyclonema
as a valid genus and compared it to his recent genus Hyalopecten.
Syncyclonema was classed as a subgenus of Pecten by Woods
(1902, p. 145), who also thought it was probably synonymous
with Entolium (Meek, 1865, p. 478; type species by original
designation, Pecten demissus Phillips, Middle Jurassic). Stephen-
son (1941, p. 133) considered it of uncertain generic status, but
included it as a subgenus of Pecten. Arkell (1930, p. 91) made
Syncyclonema synonymous with Entolium to which he gave prior-
ity. Stewart (1930, p. 120) and Feldtmann (1951, p. 10), who
followed the same procedure, more correctly gave Syncyclonema
priority. In contrast Hayami (1965) concluded that Syncyclonema
is distinct from Entolium. Both Dall (1898, p. 752) and Cox
(1952, p. 35) thought the genus too poorly known to be certain
of its status. Because of the inadequacy of Hall & Meek’s (1856)
original description of Pecten rigida for detailed systematic com-
parisons the conclusions of Dall and Cox are the most correct.
So much difference of opinion indicates the need for a rede-
scription and discussion of the morphological features of P. rigida.
The new data provides a base for considering the relationships
between Syncyclonema and other similar small pectinid genera
with which it has often been compared.
ACKNOWLEDGEMENTS
Comparison of Syncyclonema with other genera through the
loan of material, provision of information, and discussion, has
been facilitated by the following persons whose assistance is
gratefully acknowledged: The late Dr. L. R. Cox, Mr. C. P.
Palmer and Mr. N. J. Morris, British Museum of Natural History,
London; Mr. A. G. Brighton, Sedgwick Museum, Cambridge; Dr.
1967 REVISION OF SYNCYCLONEMA | RV 3
J. M. Edmonds, University Museum, Oxford; Mr. G. F. Willmot,
Yorkshire Museum, York; Dr. W. J. Clench, Museum of Com-
parative Zoology, Harvard University, Cambridge, Massachusetts;
Dr. Copeland MacClintock and Mr. Percy Morris, Peabody Mu-
seum, Yale University, New Haven, Connecticut; Prof. N. D.
Newell, American Museum of Natural History, New York, New
York; Dr. C. F. Kilfoyle, New York State Museum, Albany, New
York; Prof. H. G. Richards, Academy of Natural Sciences, Phil-
adelphia, Pennsylvania; Drs. E. G. Kauffman and Joseph Rose-
water, and Mr. W. J. Byas, United States National Museum,
Washington, D.C.; Dr. Peter Rodda, Texas Bureau of Economic
Geology, Austin, Texas; Prof. W. P. Popenoe, University of
California, Los Angeles, California; Dr. Koichiro Ichikawa, Osaka
City University, Osaka; and Dr. Itaru Hayami, Geology Depart-
ment, Kyushu University, Fukuoka, Japan. Messrs S. N. Beatus
and D. L. Homer took most of the photographs accompanying
this paper.
Doctors Kauffman and K. M. Waage, Peabody Museum, Yale
University, and Dr. G. R. Stevens and Mr. P. A. Maxwell, New
Zealand Geological Survey, kindly read the text and made valu-
able suggestions. Specimens of Syncyclonema halli were collected
and described as part of a dissertation for the Degree of Doctor
of Philosophy at Yale University, while I was on leave from the
New Zealand Geological Survey and was a holder of a New Zea-
land Department of Scientific and Industrial Research National
Research Fellowship.
Specimens mentioned and figured in this paper are held at
the following institutions:
Academy of Natural Sciences, Philadelphia (ANSP)
American Museum of Natural History (AMNH)
British Museum of Natural History (BMNH)
Museum of Comparative Zoology, Harvard University (MCZ)
Osaka City University (OCU)
Peabody Museum of Natural History, Yale University (YPM)
Texas Bureau of Economic Geology (BEG)
U. S. National Museum (USNM)
World Mollusca Collection, New Zealand Geological Survey
(NZGS-WM )
Yorkshire Museum
4 Postilla YALE PEABODY MUSEUM No. 110
DISCUSSION OF THE STATUS OF SYNCYCLONEMA
AND ITS EYPE SPECIES PECLEN TArET
HISTORY OF THE TYPE SPECIES OF SYNCYCLONEMA
Meek (1864a, p. 31) proposed the genus Syncyclonema, with
Pecten rigida Hall & Meek (1856, p. 381, pl. 1, figs. 4a-c; non
Pecten rigida Sowerby, 1818, p. 5, pl. 205, fig. 8; = Pecten halli
Gabb, 1861, p. 214), Upper Cretaceous, as the type species by
original designation. Meek, on p. 31, used the spelling Syncyclo-
nema in the heading to a short description and discussion of the
genus as follows: “195 = SYNCYCLONEMA, Meek. Type Pecten
rigida, Hall & Meek”, but on an earlicr page in a check list he
(p. 7) used a second spelling, “195. Sincyclonema_rigida,
(Hall & Meek) Meek. Dak.”. It is important to note that Meek
used the spelling Syncyclonema in his generic description and
designation. This spelling was used consistently by Meek in later
publications and on labels accompanying collections he examined.
Most other workers since Meek have preferred the spelling
Syncyclonema. It is therefore concluded that the spelling Sincy-
clonema was probably a typological or editorial error, and under
the terms of the first reviser, Article 24 of the “ International
Code of Zoological Nomenclature” (Stoll, et al., 1961), Syncy-
clonema is designated as the valid spelling.
Pecten rigida was erected by Hall & Meek (1856, p. 381) for
a small pectinid collected by F. V. Hayden from the upper Pierre
Shale at Sage Creek, South Dakota. Gabb (1861) noted the
preoccupation of the name rigida by Pecten rigida Sowerby (1818),
a quite different species, and renamed Hall & Meek’s species as
Pecten hallii Gabb. Following the recommendation of the Inter-
national Commission of Zoological Nomenclature (Stoll, et al.,
1961, p. 107) the ending -i rather than -/i is used here. Gabb’s
new name was ignored by Meek (1864a, p. 31) when he proposed
the genus Syncyclonema, although he clearly knew that the name
rigida was preoccupied and his species distinct from Sowerby’s.
Meek (1876) later redescribed rigida and gave a more complete
diagnosis of the genus Syncyclonema, but placed Gabb’s name
halli in synonymy under his rigida. Since 1876 the only other
work of importance discussing this species is that of Whitfield
1967 REVISION OF SYNCYCLONEMA 5
(1880) who described and illustrated specimens of S. halli
(USNM 12272) from the Cheyenne River, Black Hills.
Whitfield (1901, p. 424) reported that the American Mu-
seum of Natural History held “the Gen. and Sp. Type. Syncyclo-
nema Meek rigidum ... H. & M.”, from Sage Creek, Wyoming
(AMNH 5351/1). The full label accompanying this collection,
now numbered as AMNH 9347, lists “Syncyclonema_ rigida,
Ee& Mesp: YPE. Mem A; Ac. Scic& Arts, vol. 5; p: 381, pl;
fig. 4, Cretaceous No. 4, Fort Pierre Gp. Sage Creek, Nebraska
(Wyoming).” Professor N. D. Newell kindly examined the col-
lection and reported (written communication Oct. 17, 1966) that
the specimens of S. halli “do not agree in detail with the original
figures” of Hall & Meek. Comparison of photographs (pl. 1, figs.
1-3) of right and left valves most closely resembling Hall & Meek’s
drawings, here reproduced as figs. 6 and 7, pl. 1, support Profes-
sor Newell’s conclusion. Hall & Meek’s drawings were probably
idealized by the artist, especially as the specimens are small. Gross
similarities are evident, but differences in size, shape and orna-
ment make it impossible to be sure that the specimens in AMNH
9347 are the originals from which the drawings were made.
Because Hall & Meek’s original collections were dispersed I
examined collections at the United States National Museum,
Washington, and the Academy of Natural Sciences, Philadelphia,
but found no specimens matching the original drawings. Collec-
tion USNM 347 is listed (Schuchert, 1905, p. 636) as containing
“Cotypes” of S. halli. As this collection is from “The Cheyenne
and Moreau Rivers, South Dakota”, and not from Sage Creek,
it cannot be the original collection of Hall & Meek. Consequently,
the specimens of S. Aalli in this collection are not cotypes but
probably include all or some of the specimens on which Meek
(1876) based his redescription of the species and possibly his
figures (1876, pl. 16, figs. 5a, b; but see below). Correspondence
with Dr. Kilfoyle, New York State Museum, Albany, and Pro-
fessor Popenoe, University of California, Los Angeles, established
that these institutions do not hold collections likely to contain
Hall & Meek’s original specimens of S. halli.
Collection USNM 347 includes three specimens of S. halli; a
left valve (347a), a partly buried valve with concentric sculpture
(347b), and a partly buried interior showing fine radial striae
(347c).
6 Postilla YALE PEABODY MUSEUM No. 110
Specimen 347a is labeled as being the original of fig. 5b of
the pl. 16 of Meek (1876) (pl. 3, fig. 4). But this specimen,
and also the drawing, is a left valve and not a right valve as
stated in Meek’s caption. Judging from his descriptions Meek
(1876, p. 27) probably mixed the captions of his figures Sa and
5b. In addition, correspondence of the specimen with fig. Sb is
unlikely because the specimen retains most of the shell on the
ventral half of the valve, and it lacks the fine radial striae and
widely spaced concentric ornament shown on Meek’s illustration
of the steinkern (pl. 1, fig. 4). The differences are too great to be
accounted for by artistic license, for even though Meek idealized
many of his illustrations to varying degrees, he usually recorded
gross morphological characteristics and imperfections. In many
cases I have been able to identify positively Meek’s specimens
because of imperfections recorded on the drawings. Althougi
USNM 347a is unlikely to be the original of fig. 5b, the original
specimen should be located to prove positively this contention.
There is no trace of the original of Meek’s (1876, pl. 16)
fig. 5a in USNM 347, and this specimen also appears to have been
lost.
Although it is not possible to be absolutely certain that the
specimens represented by the original illustrations of Hall & Meek
are conspecific with the specimens of S. halli in AMNH 9347
their gross similarity strongly suggests that they are conspecific
(see pl. 1, figs. 1-3, 6, 7). Examination of Meek’s (USNM 347)
and Whitfield’s (1880, USNM 12272, pl. 1, fig. 8) specimens
shows they are conspecific with each other and also with the
specimens in AMNH 9347 and collections made by Professor
K. M. Waage and myself from the type area of the Fox Hills
Formation. Meek’s identification and labeling as Pecten rigida
of specimens in USNM 347, which were collected from the “Chey-
enne and Moreau Rivers’, a locality lying within the type area of
the Fox Hills Formation, gives additional support to my conclu-
sion that Hall & Meek’s species concept includes the specimens
in the collections discussed above.
No holotype or lectotype has been designated for S. halli.
In order to fix the concept of the species, and genus, it is neces-
sary to select a lectotype. Although it can never be certain that
AMNH 9347 is the original collection studied by Hall & Meek,
1967 REVISION OF SYNCYCLONEMA 7
or that it contains the originals of their illustrations, all the evi-
dence indicates that it most probably is the original collection.
Consequently, the almost complete right valve (AMNH 9347/1.1;
pl. 1, fig. 3) from this collection, 4 mm long and 5 mm high,
showing nine shallow concentric plicae on the ventral half of the
shell, and a distinct byssal notch, but with the anterior auricle
incomplete, is here selected as the lectotype.
SYSTEMATICS OF SYNCYCLONEMA AND ITs TYPE SPECIES
GENUS SYNCYCLONEMA
AUTHOR. Meek, 1864a, p. 31, 7.
TYPE SPECIES. By original designation, Pecten rigida Hall & Meek
(1856, p. 31, pl. 1, figs. 4a-c; non Pecten rigida Sowerby, 1818,
p. 5, pl. 205, fig. 8; = Pecten halli Gabb, 1861, p. 214), Sage
Creek, South Dakota, Pierre Shale, Upper Campanian-Maastrich-
tian.
EMENDED DIAGNOSIS OF SYNCYCLONEMA. The following diag-
nosis is based on study of the type species halli (see below):
Small, subequivalve, subequilateral. Shell of vitreous appear-
ance, thin, of three layers: thin outer homogeneous or prismatic
layer, middle layer of zigzag lamellar structure, and thin inner
complex cross-lamellar layer. Ornament sub-macroscopic, except
on ears, of fine non-punctate diverging radial striae, fine growth
striae, and coarser irregular growth lamellae tending to give
reticulate pattern. Radial striae strongest at ventral margin and on
dorsal flanks of disc of shell, sometimes absent on center of disc.
Concentric lamellae strong on ears. Interior of shell sometimes
with low faint rounded concentric ridges and fine radial striae.
Concentric undulations sometimes evident on external surface,
particularly on the right valve.
Anterior auricle equal to or significantly larger than the poste-
rior. Anterior auricle of the right valve distinctly separated from
disc of shell, fasciole very narrow, and byssal sinus deep, open
V-shaped. No ctenolium. Dorsal margin of right valve overlaps
that of the left valve. Each auricle with one thin cardinal crus
below the ligament band, that on the posterior auricle of each
8 Postilla YALE PEABODY MUSEUM No. 110
valve extending usually only about two-thirds of the distance to-
wards the posterior margin (pl. 3, figs. 1, 5). One relatively long
strong tooth-like process on either side of the resilifer pit of the
right valve (pl. 2, fig. 5; pl. 3, figs. 2, 5). No auricular crura.
Adductor muscle impression small, subcircular, sited above two-
thirds the height of shell adjacent to basal part of posterior auricle.
Pallial line continuous.
DISCUSSION. Several morphological features of the type species,
S. halli, require discussion before the status of Syncyclonema is
fully clarified.
1. Byssal sinus. Syncylonema halli has a deep byssal sinus
on the right valve (pl. 2, figs. 1, 5). Careful examination of
the internal and external surfaces of right valves provided no
evidence of a ctenolium at any stage of growth. S. halli was prob-
ably a free swimming pectinid. Stewart (1930, p. 120) thought
the small specimens of S. halli described by Hall & Meek (1856)
and Meek (1876) might be juveniles of a species of Entolium,
but growth lines show the presence of a relatively large byssal
auricle at all stages of growth, and for this reason S. halli cannot
be classed in Entolium (see below). The normal occurrence of
specimens 10 to 13 mm long, but none larger than this, suggests
that the largest specimens are adults of a small species.
2. Musculation. The adductor muscle impression is weakly
impressed and was observed on only a few specimens. It is small,
subcircular, sited postero-dorsally, with its base at or above two-
thirds of the height of the shell adjacent to the basal part of
the posterior ear (pl. 2, fig. 3; pl. 3, fig. 6). Whitfield (1880, pl.
7, fig. 1) illustrated the adductor scar which, as he noted, occurs
in an unusual position. Examination of his specimen (USNM
12272; pl. 1, fig. 8) shows that the impression is partially masked
by a pattern of vermiculated markings. The pallial line sometimes
coinicides with the contact of the inner and outer shell layers
and has a small oval inflated impression near its postero-ventral
extremity (pl. 3, fig. 6).
3. Auricular crura. No auricular crura are developed, although
a few right and left valves have the internal surface of the anterior
ear slightly thickened along the junction with the main disc of the
shell.
1967 REVISION OF SYNCYCLONEMA 9
4. Ornament. Meek (1864a, p. 31), in his original diagnosis
of the genus, described the ornament of the right and left valves
as “surface with fine obscure concentric striae and sometimes on
the right valve, small rounded concentric ridges.” In his (Meek,
1876, p. 26) later, more detailed diagnosis he stated “surface
showing only concentric striae, and sometimes stronger, regularly
defined concentric ridges on the right valve.” Although he uses
the word “sometimes” in this description, on p. 27 he stressed
the discrepancy of ornament between the valves.
In their original description of S. halli Hall & Meek (1856)
described but did not emphasize the discrepancy in ornament.
Clearly the emphasis should have been on the similarity of
the ornament on each valve, and on the uncommon occurrence
of weak concentric plicae. Misinterpretation of Meek’s diagnosis
and discussion has undoubtedly contributed to the uncertain status
of the genus. Most of the specimens from the Fox Hills Forma-
tion, admittedly younger stratigraphically than those of Hall &
Meek (1856) from Sage Creek, have similar ornament on each
valve. Weak concentric ridges are sometimes present on the inner
surface of the shell of either valve (pl. 3, fig. 4), and tend to
show up more strongly on steinkerns. Strong concentric lamellae
are rarely developed. The lamellate ornament, like the internal
concentric ridges, tends to be accentuated by the removal of the
thin outer prismatic layer of the shell.
The concentric ridges are more regular on the steinkern illus-
trated by Whitfield (1880, pl. 7, fig. 1; see pl. 1, fig. 8), and on
the right valves in AMNH 9347 (pl. 1, figs. 1, 3), than on any
specimen collected from the type area of the Fox Hills Formation.
Compared with the overall similarity of the other morphological
features, the difference in this one character is not considered of
species rank, particularly as the concentric ridges are stronger on
small than large specimens (compare pl. 1, figs. 1, 3, 8, with
pla, fig. 4).
COMPARISONS. Other virtually smooth small pectinids assigned
to Pecten, Camptonectes, and Syncyclonema, may also be con-
generic with S. halli. Possible Upper Cretaceous species include
Pecten (Camptonectes) kaufmanensis Stephenson (1941, pl. 21,
figs. 7-9), P. (C.) cavanus Stephenson (1952, pl. 19, fig. 7), P.
10 Postilla YALE PEABODY MUSEUM No. 110
(Syncyclonema) travisanus Stephenson (1941, pl. 22, fig. 1), and
specimens placed under Pecten simplicius Conrad (e.g. Wade,
1926, pl. 20, fig. 7). Inclusion of these species would necessitate
modifying the diagnosis to cover species with ornament varying
from smooth to with strong concentric striae, with the byssal notch
deep to moderate, and the fasciole narrow to moderately wide.
Syncyclonema halli (Gabb)
(Pl. thes. 1-95 pl. 2; figs. 1=55ple 35 fies: 1-4 254-bp
Pecten rigida Hall & Meek, 1856, p. 381, pl. 1, figs. 4a-c (non
Sowerby, 1818, p. 5, pl. 205, fig. 8).
Pecten hallii Gabb, 1891, p. 214. (Nom. nov. for P. rigida Hall
& Meek).
Sincyclonema rigida (Hall & Meek). Meek, 1864a, p. 7.
Syncyclonema rigida (Hall & Meek). Meek, 1864a, p. 31.
Meek, 1876, p: 27, pl. 16, figs. 5a, b. Whitheld; 1880; pa3sae
ple 7, tig. A:
LECTOTYPE. Here selected (p. 7), AMNH 9347/1.1, a right
valve, 4 mm long and 5 mm high (pl. 1, fig. 3), Sage Creek,
South Dakota, Pierre Shale, Upper Campanian-Maastrichtian.
MATERIAL. One hundred and seventeen specimens, including eight
articulated or displaced bivalved.
OCCURRENCE. In the type area of the Fox Hills Formation S. halli
is virtually restricted to the Timber Lake Member (Waage, in
press).
The species, recorded by Fisher, et al. (1960), as Syncyclo-
nema hallii, from the lower part of the Pierre Shale and in the Sego
Sandstone in western Colorado and eastern Utah, and by Griffitts
(1949) as S. rigida, from the “Rocky Ridge sandstone member
of the Hygiene zone” of the Pierre Formation in Colorado, is
apparently rare in the Upper Cretaceous sequences of the Western
interior. It is found mainly in sandstone units.
DESCRIPTION. Small, length of specimens 3.5 to 13.2 mm, subequi-
valve, equilateral to slightly inequilateral, compressed, valves
equally inflated. Orbicular, with height, width of one valve, length
1967 REVISION OF SYNCYCLONEMA ial
of dorsal margin (between extremities of ears), and anterior
lenothyrespectively, 1OI4 ton1292 (n=287 x11. 7%), 4:6. t0
131325) x— 911%), 482) 1064.6. (n= NOY x=5 4.9%). and
45 to 55.9 (n=28, x=49.2% ) per cent of length, and length of
anterior ear 50 to'63.2) (n=19, x=55.7-% ) per cent of length of
dorsal margin. Umbones weakly prosogyrous, project slightly above
dorsal margin. Antero- and postero-dorsal margins of the disc of
shell straight or slightly concave, form an angle of 87.5 to 100
degrees, and meet the rounded ventral margin at distinct angula-
tions. Dorsal margins of ears straight, intersect at a small angle,
the anterior is more steeply inclined. Margin of right valve, espe-
cially that of the anterior ear, projects above and overlaps the
margin of left valve. Anterior ear equal to or larger than posterior.
Ears of left valve, and posterior ear of right valve, weakly delimited
from disc of shell, although the margin of disc becomes overhang-
ing ventrally, with straight or rounded anterior or posterior margins
which form a rounded or angled junction with the dorsal margin
of the ear. Anterior ear of right valve sharply delimited from the
overhanging margin of the disc, with a narrow fasciole at base, at
the ventral end of which is a narrow moderately deep V-shaped
byssal sinus. Ctenolium apparently lacking.
Ornament similar on both valves, of submicroscopic vermiculat-
ing Camptonectes-striae, 40 to 50 per millimeter at ventral
margin, fine growth striae and coarser irregular growth lamellae
tending to give a reticulate pattern. Striae are sometimes very weak
on the center of disc and, with the growth striae, are often very
strong on the antero- and posiero-dorsal flanks of disc and some-
times on ears. Either the striae or growth lamellae may dominate
on the ears. Internal surface of shell sometimes with irregular or
regular shallow rounded concentric costae and fine radial striae.
Resilifers triangular, internal, do not extend to ventral margin
of hinge-plate. Resilifer of right valve bordered on either side by a
short strong tooth-like process which extends the length of the
resilifer and fits into sockets on each side of the resilifer of the left
valve. Ligament groove narrow, submarginal, extends most of
length of ears, bordered below by a weak cardinal crura. No auric-
ular crura. Pallial line continuous, extending in a loop across shell
at about one-quarter of the height above base, becomes indefinite
antero-dorsally at base of the fasciole. The pallial line has a smali
1 Postilla YALE PEABODY MUSEUM No. 110
subquadrangular scar situated at about one-third the height of the
shell; and a large subcircular adductor scar is situated near the
base of the posterior ear in the dorsal quarter of the shell. Muscle
scars on the left valve unknown.
Ostracum less than 0.2 mm thick, of three layers. A very thin
outer layer, probably prismatic, bearing the Camptonectes striae,
a translucent middle layer, apparently of zigzag lamellar structure
(Béggild, 1930, p. 267), that thickens towards the ventral margin,
and an inner white layer of complex cross-lamellar structure that
is thickest in the umbonal region and ceases within one to two
millimeters of ventral margin (pl. 2, fig. 1). Outer surface vitreous,
but with irregularly distributed, radially elongated patches of matt
appearance (pl. 2, fig. 4).
DISCUSSION. Left and right valves of S. halli are equally inflated
and their other measurements have approximately the same range
of values and means. In spite of the extremely fragile shell
few specimens from concretions in the type area were broken
during deposition. Complete specimens are very difficult to extract
and the ears are especially prone to damage. At Yale loc. 288,
Solen, North Dakota, where the sediment is a limonite-cemented
medium-grained sandstone with little argillaceous matrix, many
specimens were broken during transportation. The tripartite layer-
ing of the shell described above requires confirmation by thin
section studies. As interpreted it is similar to the shell of “P.
textorius (Liassic)” of Bgéggild (1930, p. 267). The very thin
outer prismatic layer bears the Camptonectes-like striae and,
although always present on well preserved specimens, it is easily
removed by abrasion, weathering or extraction. The shell then
appears smooth or with concentric lamellae only. Species of
Camptonectes recorded in the literature as being smooth and
striate should be re-examined to ascertain that the outer layer, if
this is characteristic of the genus, has not been lost, especially in
the case of small species.
Whitfield (1880, pl. 7, fig. 1) illustrated a different pattern
of muscle scars on a steinkern from “the forks of the Cheyenne
River, Black Hills.” He commented on the unusual position of
the muscle scar. Examination of recent pectinid species held in
the collections of the Peabody Museum, Yale University, showed
1967 REVISION OF SYNCYCLONEMA 13
that some, for example Cyclopecten (Delectopecten) vitreus
(Chemnitz), Pseudamussium striatum (Miller), and P. septem-
radiatum (Miller), have an elongated or oval scar in a com-
parable position close to the base of the posterior ear of the right
valve. The ventral small subquadrangular scar in the pallial line
is present on several specimens and seems to be a valid scar. It
may represent a gill suspensory attachment (Newell, 1937, p. 21).
COMPARISONS. Specimens of Pecten (Camptonectes) kaufmanensis
Stephenson (1941, pl. 21, figs. 7-9) and P. (C.) cavanus Stephen-
son (1952, pl. 19, fig. 7) closely resemble S. halli. Other speci-
mens from Gulf and Atlantic Coastal Plains sequences classed
under Pecten or Syncyclonema resemble S. halli in shape and size
but apparently lack the fine Camptonectes-striae. Some, for exam-
ple P. (Syncyclonema) travisanus Stephenson (1941, pl. 22, fig.
1), show traces of radial ornament, while others, like P. simplicius
Conrad (Wade, 1926, pl. 20, fig. 7) and the right valve of P.
travisanus (Stephenson, 1941, pl. 22, fig. 2), have relatively
strong lamellae like S. halli when its outer prismatic layer is lost.
THE FAMILY PLACEMENT OF SYNCYCLONEMA
Pectinid-like genera have been classified into either the
Pectinidae Rafinesque (1815) or the Amusiidae Ridewood (1903).
The placing of genera in the Amusiidae is primarily based on
anatomy (Cox, 1952, p. 33), and in the absence of anatomical
information the classification of some fossil and Recent genera
is difficult, especially small, thin-shelled, weakly ornamented
forms which possess a small byssal notch and lack internal ribs
and muscle impressions. Most paleontologists have accepted only
one family, the Pectinidae (Marwick, 1928; Grau, 1959). Newell
(1965, p. 18) follows this procedure in his proposed classification
of the Bivalvia for the “American Treatise of Invertebrate
Paleontology.”
Korobkov (1960) subdivides the Pectinidae into five sub-
families, including the Amusiinae and Pectininae. Detailed revi-
sion of the morphology and anatomy of pectinid genera is required
14 Postilla YALE PEABODY MUSEUM No. 110
to confirm the validity of some of these subfamilies. A new sub-
family proposed by Korobkoy, the Entoliinae, was raised to
family rank by Newell (1965). Characteristics of the family
include an equivalve or subequivalve inflated shell, weak orna-
mentation, a small or no byssal sinus, and usually strong auricular
and cardinal crura. The following is a translation of the diagnosis
of the subfamily Entoliinae given by Korobkov (p. 83) as pre-
pared by the Translation Service of the New Zealand Department
of Internal Affairs:
“The shell is prosocline or acline, often gaping; the ears of the
left valve are raised, those of the right valve are almost identical
and not raised, the resilifer cavity is almost symmetrical and com-
paratively small; dentate ridges are strongly developed on the
ears, at their base they appear more weakly; the byssus notch is
entirely absent or can be seen only in the early stages of develop-
ment; the outer surface is smooth or has regular concentric
riblets, more rarely having radial striae. Carboniferous to
Cretaceous.”
Genera included by Korobkov in the Entoliinae are Perno-
pecten Winchell (1865), Entolium Meek (1865), and doubt-
fully Syncyclonema Meek (1864a). Other possible members are
Pseudentolium Cox (1948; not synonymous with Eburneopecten
as suggested by North, 1951) and Creniopleurium Feldtmann
(1951). Somapecten Kimura (1951), Jurassic, should perhaps
be included, although it has a distinctive interlocking hinge appa-
ratus and may be an aberrant offshoot of a pectinid or entoliid
stock.
Recognition of the Pectinidae and Entoliidae separates two
morphologically different groups of genera, chlamyiid-like and
entoliid-like respectively, and is supported by the writer. Detailed
paleontological studies are required to prove whether the Entoli-
idae is monophyletic or polyphyletic. The occurrence throughout
the late Mesozoic and Tertiary of pectinid genera, e.g. Lentipecten
Marwick (1928), and amusiid-like genera, closely resembling
entoliids suggests that the Entoliidae may be polyphyletic and
include convergent end members of branches from a pectinid stem.
The morphology of Syncyclonema indicates placement in the
Pectinidae and clearly excludes it from the Entoliidae, as is shown
in the next section.
1967 REVISION OF SYNCYCLONEMA 15
ENTOLIUM, AND A COMPARISON WITH
SYNCYCLONEMA
GENUS ENTOLIUM
AUTHOR. Meek, 1865, p. 478.
TYPE SPECIES. By original designation, Pecten demissus Phillips
(1829, p. 124, 140, pl. 6, fig. 5), Middle Jurassic, England and
Europe.
DISCUSSION. Diagnoses of the genus Entolium (Arkell, 1930, p.
91; Cox, 1952, p. 34) stress external morphological features,
especially the relatively smooth thin shell, dorsally projecting
auricles (particularly on the left valve), and the lack of a byssal
notch (at least on adult specimens). The external characteristics
as shown by the holotype of E. demissum (pl. 3, fig. 3) are rather
constant, although the shape of a species may be extremely
variable (Staesche, 1925, p. 100).
Less is known of the internal features of species of Entolium.
One of the three groups of Staesche (1925), that of E. cingulatum
Goldfuss, has fine internal ridges on the main disc of the shell
close to each auricular margin. The generic significance of these
ridges is uncertain. Most species possess strong auricular crura
and one cardinal crus on each auricle close to the dorsal margin
(Korobkov, 1960, p. 83; E. sanchuense, Hayami, 1965, p. 315;
E. fossatum, Marwick, 1953). The auricular crura in part reflect
the strong grooves which separate the auricles from the disc of
the shell on many species. Some species appear to lack cardinal
crura, although others have two strong cardinal crura on the right
valve (E. irense McLearn, 1933, pl. 1, fig. 10; NZGS-WM 5403)
or possibly two crura and tooth-like processes on each side of
the resilifer, [E. orbicularis (Sowerby) Woods, 1902, pl. 27,
fig. 14].
I attempted to obtain suitable specimens to clarify the hinge
morphology of the type species E. demissum. Unfortunately,
these were not available from the collections of the British
Museum, Oxford University, or Cambridge University. Consider-
able work is required before the taxonomy of entoliids is clear.
16 Postilla YALE PEABODY MUSEUM No. 110
COMPARISON OF ENTOLIUM with SYNCYCLONEMA. Many
authors, as summarized in the Introduction (p. 2), have sug-
gested synonymizing Syncyclonema under Entolium. The inade-
quacy of the original descriptions and illustrations of S. halli
undoubtedly has led workers to assume that it had approximately
equal auricles and lacked a distinct byssal sinus.
Nevertheless, Syncyclonema is easily distinguished from Ento-
lium by its chlamyiid rather than orbicular shape, the possession
of a deep byssal sinus, which is lacking on Entolium, and the
occurrence of radial ornament on the auricles, which is also not
present on Entolium. Internally, Entolium lacks the distinct tooth-
like processes present on either side of the resilifer on the right
valve of Syncyclonema. Other differences in internal morphology,
for example musculation, may prove to be significant.
The differences prove that Syncyclonema should not be syno-
nymized under Entolium.
COMPARISON OF SYNCYCLONEMA WITH
OTHER SMALL PECTINID GENERA
Syncyclonema superficially resembles a number of pectinid
genera and this similarity has been a source of confusion. In
particular, Syncyclonema has been compared with Camptonectes
Agassiz, Eburneopecten Conrad, Pectinella Verrill, Micronectes
Ichikawa & Maeda, Hyalopecten Verrill, and Pseudamussium (see
below).
Study of these genera has been hampered by a lack of knowl-
edge of morphological features and variation within the genera,
particularly as most of the genera are known largely from the
type species.
Shape and ornament are the characters used to separate most
pectinid genera. Poorly known and little used morphological
features of potential systematic importance include shell struc-
ture, details of muscle impression patterns, hinge morphology —
especially the number and length of the cardinal crura and
whether or not the dorsal one bears the ligament— and the
consistency and length of the tooth-like process on either side
of the resilifer of the right valve.
1967 REVISION OF SYNCYCLONEMA 11 7/
To facilitate comparison of several of the above genera with
Syncyclonema the opportunity is taken in the following sections
to redescribe the type species of the poorly known genera Pec-
tinella, Hyalopecten, Pseudamussium Morch, and “Pseudamus-
sium” H, & A. Adams. The formal systematic data for the genera
and their type species are presented and discussed where appro-
priate. Presentation of full synonymies of the type species is not
practicable for this paper.
1. GENUS CAMPTONECTES
AUTHOR. Agassiz, in Meek, 1864b, p. 28, 39.
TYPE SPECIES. By original designation, Pecten auritus Schlotheim
(1813; = P. lens Sowerby, 1818), Middle and Upper Jurassic,
England and Europe.
DISCUSSION. The authorship of Camptonectes is controversial.
Meek (1864b, p. 39) clearly indicates that the concept of the
genus, and the virtual selection of a type species, was due to
Agassiz (MS) and under the Rules of Zoological Nomenclature
(Stoll, et al., 1961, p. 49, Art. 50) the name should be accredited
to Agassiz. Stoliczka (1871, p. 425) was the first to use the word
type with reference to P. lens.
COMPARISON WITH SYNCYCLONEMA. Typical small and large
species of Camptonectes are clearly distinguished from Syncyclo-
nema by their macroscopic and frequently punctate (but see Cox,
1952, p. 22) “Camptonectes’” ornament, large byssal ear with a
wide fasciole, very deep byssal sinus, strong ctenclium, and thick
shell (see pl. 4, fig. 3).
The internal features of species of Camptonectes are poorly
known. Cox (1952, p. 22) states that cardinal crura are lacking
on the type species C. auritus, but they are present on Pecten
(Camptonectes) moodyi Stephenson (1952, p. 79). A small
specimen of C. auritus, prepared for the writer by Dr. L. R. Cox
and his assistant, Mr. C. P. Palmer, shows a weak cardinal crus
on each auricle of the right valve (pl. 4, figs. 1, 3). On the
internal surface of the byssal auricle this specimen also has a
18 Postilla YALE PEABODY MUSEUM No. 110
strong ridge extending in an arc from the umbone to the antero-
ventral margin of the auricle. This ridge is strongest antero-
ventrally and coincides on the external surface with the dorsal
margin of the wide fasciole. Dr. Cox (written communication,
June 29, 1965) describes the hinge features as follows: “There
is a very weak cardinal crus on each side close to the hinge margin
and best developed some distance from the beak. In addition,
there is a strong ridge running from the beak to the lower margin
of the part of the anterior auricle above the byssal notch. This
ridge is also well seen in a second specimen. A comparable but
weaker ridge is present in some Recent specimens of Chlamys.
Auricular crura, running from the beak along the lower margin
of complete auricles, are absent.” The anomaly of no crura on
some specimens and weak crura on small specimens may be
accounted for by the degeneration and loss of crura with increas-
ing size and age.
The general position of many small, weakly ornamented,
species placed in Camptonectes is uncertain. Some may belong to
Micronectes and others to Syncyclonema.
2. GENUS EBURNEOPECTEN
AUTHOR. Conrad, 1865, p. 140.
TYPE SPECIES. By monotypy, Pecten scintillatus Conrad (1865,
p. 140, pl. 10, fig. 4), Moodys Branch Marl, Jackson Group,
Upper Eocene, Garlands Creek, Clarke County, Mississippi.
COMPARISON WITH SYNCYCLONEMA. Externally Syncyclonema
very closely resembles species of Eburneopecten, which differ
significantly only by the presence of a strong ctenolium, prominent
radial costae, a more distinct fasciole on the anterior ear of the
right valve, and less prominent lamellae on the auricles. The dis-
covery by Stenzel, et al. (1957, p. 85), of specimens of Eburneo-
pecten lacking radial ornament on the anterior auricle suggests
that this feature may be of specific rank only.
Eburneopecten differs from Syncyclonema mainly in internal
morphology. Eburneopecten has two cardinal crura on each auricle
of the right valve and on the anterior auricle of the left valve,
PLATE SECTION
PEATE 1
Syncyclonema halli (Gabb)
Fic. 1. Syntype, AMNH 9347/1.2. Exfoliated right valve, anterior
auricle incomplete. Pierre Shale, Sage Creek, Upper Cretaceous. x 10.
Fic. 2. Syntype, AMNH 9347/1.3. Incomplete steinkern of a left
valve. Pierre Shale, Sage Creek, Upper Cretaceous. « 10.
Fic. 3. Lectotype, AMNH 9347/1.1, here selected. Right valve with
an incomplete anterior auricle. Most of shell removed, remainder lacking
outer shell layer. Pierre Shale, Sage Creek, Upper Cretaceous. x 10.
(Photographs for figs. 1-3 kindly supplied by Prof. N. D. Newell).
Fic. 4. Fig. 5b of Meek (1876, pl. 16), a left valve and not a right
valve as stated in the caption. Supposedly in USNM 347, Pierre Shale,
Cheyenne and Moreau Rivers, South Dakota, Maastrichtian. Not found,
assumed lost. * ca. 2.
Fic. 5. Fig. 5a of Meek (1876, pl. 16), a right valve and not a
left valve as stated in the caption. Anterior auricle probably incomplete.
Supposedly in USNM 347, not found, assumed lost. * ca. 2.
Fics. 6, 7. Figs. 4c and b respectively of Hall & Meek (1856, pl. 1),
left and right valves respectively. Pierre Shale, Sage Creek, Upper Cre-
taceous. < ca. 2. (Photographs kindly supplied by John Howard, Peabody
Museum, Yale University).
Fic. 8. USNM 12272; steinkern of a right valve, anterior auricle
incomplete, showing concentric ridges and fine radial striae. The original
of Whitfield, 1880, pl. 7, fig. 1. Forks of the Cheyenne River, Black Hills,
South Dakota, Upper Cretaceous. 6.
Fic. 9. YPM 24129; a left valve from Solen, North Dakota, YPM
colln. A-1409, loc. 288, Timber Lake Member, Fox Hills Formation,
Maastrichtian. « 6.
PLATE 2
Syncyclonema halli (Gabb)
Fic. 1. YPM 24122; an internal view of the shell of a right valve,
showing the inner thin white complex cross-lamellar layer and the trans-
lucent middle layer. Note the deep byssal notch and incomplete cardinal
crus on the anterior auricle. YPM A-650, loc. 73, Cucullaea Assemblage
Zone, Timber Lake Member, Fox Hills Formation, Maastrichtian. «x 6.
Fic. 2. YPM 24126; a left valve showing ornament on the auricles
and fine diverging radial striae on the margins of the disc. YPM A-1409,
loc. 288, Solen, North Dakota, Timber Lake Member, Fox Hills Formation.
<9!
Fic. 3. ANSP 31245; internal view of the postero-dorsal part of the
shell of a right valve showing the faintly impressed adductor muscle impres-
sion close to the base of the posterior auricle. Pierre Shale, Mingusville.
Montana, collector Homer Squyer, Upper Cretaceous. « 12.
Fic. 4. YPM 24127; a left valve showing ornament, particularly the
diverging radial striae on the margins of the disc. YPM A-1409, loc. 288,
Solen, North Dakota, Timber Lake Member, Fox Hills Formation. « 9.
Fic. 5. YPM 24123; interior of dorsal part of a right valve, the ante- —
rior auricle incomplete and centre of hinge damaged, showing cardinal
crura. YPM A-973, loc. 100, Cucullaea Assemblage Zone, Timber Lake
Member, Fox Hills Formation. « 12.
PLATE, 3
Syncyclonema halli (Gabb)
Fic. 1. YPM 24124; rubber latex cast of a left valve hinge showing
cardinal crura, resilifer, and lack of auricular crura. YPM A-659, loc. 73,
Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills Formation.
SS 1
Fic. 2. YPM 24125; right valve hinge, anterior ear and dorsal part
masked by matrix, showing tooth-like projections on each side of a narrow
resilifer and the lack of ctenolium. YPM A-747, loc. 226, Cucullaea
Assemblage Zone, Timber Lake Member, Fox Hills Formation. x 12.
Fic. 4. YPM 25635; right valve steinkern with some exfoliated shell
ventrally, showing radial striae and weak concentric ridges. YPM A-447,
loc. 210, Cucullaea Assemblage Zone, Timber Lake Member, Fox Hills
Formation. x 3.
Fic. 5. USNM 347; rubber latex cast of a left valve, supposedly the
original of Meek, 1876, pl. 16, fig. 5b, a right valve, showing cardinal crura
and resilifer. Compare with pl. 1, fig. 4. Pierre Shale, Cheyenne and Moreau
Rivers, South Dakota. x 4.
Fic. 6. ANSP 31241; a right valve steinkern showing postero-dorsal
adductor scar, pallial line, and postero-ventral swelling. Mingusville, Mon-
tana, collector Homer Squyer, Pierre Shale. « 12.
Entolium demissum (Phillips)
Fic. 3. Holotype, Yorkshire Museum 202. Kellaways Rock, near
Scarborough, Lower Callovian, Middle Jurassic. « 1.
PLATE 4
Camptonectes auritus (Schlotheim )
Fics. 1, 3. BMNH LL 2445; internal views taken under different
lighting of the interior of a right valve, showing ctenolium, weak cardinal
crura and ridge extending from umborie to antero-ventral extremity of the
byssal auricle. Malton, Yorkshire, probably from a “large stone quarry,
Coralline Oolite, Upper Oxfordian, Zone of Perisphinctes plicatilis’ (L. R.
Cox, letters Ames 2511965) =< 129:
Fic. 6. BMNH LL 2445; exterior of right valve. Note wide byssal
notch and fasciole, and punctate “Camptonectes’ ornament. Locality data
as above. x 1.8. (Photographs for figs. 1, 3, 6, kindly supplied by Dr.
Laken COX)
Eburneopecten scintillatus (Conrad )
Fics. 2, 4. Topotype, BEG 20726; photographs of the exterior, fig. 2,
and interior, fig. 4, of a right valve showing byssal notch, narrow fasciole,
ctenolium, radial costae on the byssal auricle, weak auricular crura,
cardinal crura, short tooth-like processes on each side of the resilifer, and
the dorsally projecting dorsal margin. Garland’s Creek, Moodys Branch
Marl, Jackson Group, Upper Eocene (see Stenzel, et al., 1957, p. 82).
Bigs ara niger4a SC 6;
Fics. 5, 7. Topotype, BEG 20725; photographs of the interior, fig. 5,
and exterior, fig. 7, of a left valve showing weak auricular crura, cardinal
crura with finely striated areas on each side of the resilifer, and large
subcentral adductor scar. Locality data as above. Fig. 5, x 6; fig. 7, & 4.
PLATE 5
Micronecies bellaturus Ichikawa & Maeda
Fic. 1. OCU MM 2339; plastic cast of the dorsal part of a right valve
showing strong radial costae on byssal auricle. Loc. 151, Azenotani — 3,
Izumi Mountains, Azenotani Shale. Hetonian Series (Campanian). x 4.
Fics. 2, 3. OCU MM 238; plastic casts of the exterior, fig. 2, and
interior, fig. 3, of a left valve, showing ornament, cardinal crura, and dorsal
triangular flat-surfaced “crura”. Locality data as above. x 6.
Fic. 4. OCU MM 239; plastic cast of a right valve showing cardinal
crus on the anterior auricle. Area around resilifer poorly preserved. Locality
data as for fig. 1. x 6.
Fics. 5, 7, 8. OCU MM 772; plastic casts of a right valve showing
large anterior auricle, deep byssal notch, wide fasciole, strong costa directly
above fasciole, the hidden ctenolium (fig. 7), the prosoclinal shape, resilifer
and cardinal crura. Loc. 115, Takinoike, Izumi-Sano City, Osaka Prefec-
ture, K. Ichikawa collector, 1962, Azenotani Shale. Fig. 5, 4; fig. 7, x 8.
Fics. 6, 9. OCU MM 246; plastic casts of a valve possibly the left,
the photographs taken under different lighting, to show ornament. Locality
data as for fig. 1. x 4.
PLATE 6
Pectinella sigsbeei (Dall)
Fics. 1, 4. Holotype, MCZ 7817; a right valve, the anterior auricle
incomplete, not whitened, showing shape, ornament, and hinge morphology.
From “off Havana’, Recent. Fig. 1, 5; fig. 4, « 10. (Photographs kindly
supplied by Dr. W. J. Clench).
Fics. 2, 3. USNM 62263; a left valve, labeled as “type fig.’d”, and
probably the matching valve of MCZ 7817, showing shape, ornament,
cardinal and auricular crura. Lat 22°10’ N, long. 82°20’ W, depth 158 fms,
Recent3)<2:8:
Fics. 5, 6, 7. USNM 503313; a left valve, showing shape, ornament,
cardinal and auricular crura. Off English Harbor, Antigua Is., 120 fms,
rough coral, Recent. Figs. 5, 7, & 2.8; fig. 6, 4.
Hyalopecten dilectus Verrill & Bush
Fics. 8, 9. Holotype, USNM 44827; matching valves, showing shape,
ornament, auricles and byssal notch. Stn 229, 1423 fms, off Maryand,
Recent <2.
PLATE 7
Hyalopecten dilectus Verrill & Bush
Fics. 1, 2. Holotype, USNM 44827; matching valves, showing hinge
morphology, byssal notch and ctenolium. Stn 229, 1423 fms, off Maryland,
Recent. « 4.
“Pseudamussium” hybridum (Gmelin)
(type species of Pseudamussium H. & A. Adams)
Fics. 3, 4, 8. USNM 131671; a small left valve showing ornament,
hinge morphology, and adductor muscle scar. From West Africa, Lea col-
lection, labeled as “probably Pecten dispar Lam.” by Dall?, Recent.
Bich se eZ ign. as:
Fics. 5, 6. USNM 131671; internal and external photographs of a
right valve. Note ornament, hinge morphology and ctenolium. Locality
data as above. X 2.
Fic. 7. USNM 131671; external view of a large left valve. Compare
ornament with that of fig. 3. Locality data as above. x 2.
=
LS
1967 REVISION OF SYNCYCLONEMA 19
but only one crus on the posterior auricle of the left valve, whereas
Syncyclonema has one crus on each auricle. The outer ends
of the ventral crura on Eburneopecten bend upwards to meet the
dorsal crura below the dorsal extremities of the auricle thus
defining a cuneiform-shaped area (pl. 4, figs. 4, 5). Those on
the left valve probably fit inside those of the right valve which are
stronger. The dorsal crura and sockets of Eburneopecten adjacent
to the resilifer are transversely striated (pl. 4, fig. 5). The tooth-
like processes on either side of the resilifer on the right valve are
short and weak on Eburneopecten (pl. 4, fig. 4), but long and
strong on Syncyclonema (pl. 3, fig. 2). Eburneopecten has dis-
tinct incipient auricular crura which are stronger on the left valve.
The shape and position of the adductor muscle impression are
different. The scar of Eburneopecten is larger and situated more
centrally (pl. 4, fig. 5) than that of Syncyclonema which is close
to the base of the posterior ear.
These internal morphological differences are sufficient to
show there is no close relationship between Syncyclonema and
Eburneopecten.
3. GENUS MICRONECTES
AUTHOR. Ichikawa & Maeda, 1958, p. 95.
TYPE SPECIES. By original designation, Micronectes bellaturus
Ichikawa & Maeda (1958, p. 98, pl. 5, figs. 13-17; see pl. 5, figs.
1-9 herein), Late Cretaceous (Campanian-Maastrichtian), Japan.
COMPARISON WITH SYNCYCLONEMA. Micronectes differs con-
siderably from Syncyclonema in external and internal morphology.
The strongly inflated valves of M. bellaturus have a distinctive
ornament of non-punctate, flat- and round-topped radial costae
and strong concentric lamellae (pl. 5, figs. 2, 6, 9). The costae
become flat-topped on the ventral part of the shell and are three
or four times wider than the narrow depressions which, together
with the corrugation of the edge of the lamellae and a pseudo-
punctate effect produced by the intersection of the lamellae and
radial grooves, become the dominant features. This ornament
resembles that of species placed by Grau (1959) in Cyclopecten
20 Postilla YALE PEABODY MUSEUM No. 110
(s.s.) and C. (Delectopecten), but is quite different from the
fine submacroscopic radial markings on the compressed valves
of Syncyclonema halli. The anterior auricle of the right valve of
bellaturus bears four to six radial costae above a very wide
fasciole, the byssal notch is deep and wide, and contrary to
Ichikawa & Maeda’s statement, there is a strong ctenolium (pl.
Dey
By these characters Micronectes closely resembles Campto-
nectes, but not Syncyclonema. Each auricle has a strong cardinal
crus. That on the left valve is separated by a narrow but deep
socket from a prominent flat-surfaced crus extending the length
of the dorsal margin (pl. 5, fig. 3). The resilifer of the right valve
is deeply sunken and appears to lack bordering tooth-like proc-
esses. In contrast, Syncyclonema lacks the dorsal flat-surfaced
crus and has tooth-like processes adjacent to the resilifer.
4. GENUS PECTINELLA
AUTHOR. Verrill, 1897, p. 68.
TYPE SPECIES. By original designation, Pecten sigsbeei Dall (1886,
p. 223, pl. 4, fig. 2), from “off Havana”, Cuba, Recent.
DISCUSSION. Verrill (1897, p. 68) gave the following generic
diagnosis.
“Shell small, thin, swollen, nearly smooth, with convex and
slightly unequal valves. Auricles very unequal, oblique, the ante-
rior larger, with a deep byssal notch in the right valve, but with-
out pectinidial teeth; posterior auricle small. The surface is smooth
except for fine lines of growth. Camptonectes sculpture is not
present. The texture is not hyaline.”
Verrill based his diagnosis of the genus on P. sigsbeei, the
only species he included in his new taxon. As the diagnosis is
inadequate for present day systematics, and is also erroneous, the
opportunity is taken to redescribe the type species. An emended
diagnosis is not given as it should await a review of species
included in the genus and other closely related taxa.
The redescription of the type species was facilitated by Dr.
W. J. Clench, Museum of Comparative Zoology, who kindly
1967 REVISION OF SYNCYCLONEMA Da
sent me data and photographs of a right valve (MCZ 7817; pl. 6,
figs. 1, 4) of sigsbeei, labeled as holotype, from “off Havana”,
and by Dr. J. Rosewater, U.S. National Museum, who kindly
sent me a left valve (USNM 62263; pl. 6, figs. 2, 3) of P. sigsbeei
Dall, from “Depth 158 fms., Lat. 22°10/N, long. 82°20’W, U.S.
Coast Survey, C. P. Patterson, supt., Gulf Stream and Gulf Mexico
Explor., USCG., S. Blake, Alex Agassiz, 1877-78”, and labeled
“type fig’d.” Dr. Rosewater also sent a larger left valve (pl. 6,
figs. 5-7) USNM 503313, from “off English Harbor, Antigua,
120 fms, rough coral.”
Pectinella sigsbeei (Dall)
(PIG, hes. 1-7)
Pecten (Pseudamussium) sigsbeei Dall, 1886, p. 223, pl. 4, fig. 2.
Pectinella sigsbeei (Dall). Verrill, 1897, p. 68.
TYPE SPECIMENS. Holotype by original designation MCZ 7817, a
right valve from near Havana, Cuba, Lat. 22°10’W, Long. 82°20’,
158 fathoms, Recent, and the probably matching left valve USNM
62263 from the same locality.
Several lines of evidence indicate that the left (USNM 62263)
and right (MCZ 7817) valves originally came from the one
bivalved specimen, and together should be treated as the holotype,
especially as these were the only valves available to Dall at the
time he described the species.
1. Measurements made on the three valves are as follows:
MCZ 7817 USNM 62263 USNM 503313
(right valve ) (left valve ) (left valve )
Length or mi 9.4 Bias)
Height Qs) 10.5 16.2
Half width — 7 322
Length of
dorsal margin 4.3 4.2 eS
Anterior length of
dorsal margin Pigs) 2.8) c. 4.4
(incomplete )
i)
i)
Postilla YALE PEABODY MUSEUM No. 110
Even though the measurements of MCZ 7817 are taken from
a negative, the coincidence of the measurements of the right valve
MCZ 7817 and the left valve USNM 62263 is noteworthy and
suggests that the two valves are from one bivalved specimen.
2. The presence of dried body tissue and ligament adhering to
the inner surface of the left valve USNM 62263 (this tissue was
later removed to improve the specimen for photography) and the
apparent presence of similar material on the hinge area of the
right valve MCZ 7817.
3. The data on the label accompanying USNM 62263 matches
that given by Dall (1886, p. 223) in his original description of the
species.
4. Dall recorded “two valves were obtained by Sigsbee”’, and
his description shows he had a left and a right valve. The right
valve (MCZ 7817) clearly matches Dall’s figure (1886, pl. 4,
fig. 2), but to my knowledge, and contrary to the label (see
above) the left valve (USNM 62263) has not been figured pre-
viously (pl. 6, figs. 1-4).
5. The extremity of the anterior auricle of both the left and
right valve is incomplete, suggesting the possibility of breakage
when conjoined.
Although Dall (1886, p. 175) notes that the “types of species
described will be found in the Museum of Comparative Zoology
at Cambridge, and in the U.S. National Museum” it is most
unusual that a collection should have been split into two parts.
However, in the case of P. sigsbeei one valve seems to have been
lodged in each institution.
Dall, in his original description, did not select a specific speci-
men as the holotype. But because the label accompanying the
right valve MCZ 7817 is marked as holotype, apparently in Dall’s
handwriting, and as Dall, in the sentence quoted in the previous
paragraph, mentions depositing types in two institutions, the desig-
nation of the holotype is taken as being by original designation.
REVISED DESCRIPTION. Small, shell thin, equivalve, inequilateral,
strongly inflated. Umbones small, project only slightly above the
dorsal margin. Antero-dorsal margin of the right auricle projects
dorsally and overlaps the margin of the left valve. Auricles of
1967 REVISION OF SYNCYCLONEMA 23
the left valve and posterior auricle of right valve not sharply
delimited from disc of valve; anterior auricle of right valve with
a very narrow fasciole. Anterior auricles much larger than the
posterior. Right valve with a deep open V-shaped byssal notch;
no ctenolium.
Auricles ornamented with fine raised concentric costae, 11-13
per millimeter, and much finer submacroscopic radial costae which
cross only the interspaces between the concentric costae. Disc of
shell appears smooth except for occasional growth lines and pauses;
but has submacroscopic, very fine, regular, raised concentric
striae, about three per 0.1 mm over entire surface of shell. Disc
crossed by faint submacroscopic radiating sulci which are im-
pressed only in the interspaces between the raised concentric
striae and give the shell a fine pseudo-punctate appearance.
Radial sulci diverge and are more distinct on the dorsal flanks
of the disc. Radial sulci about one-fourth to one-sixth of the
width of the flat-crested interspaces, and about four to six per
0.1 mm.
Left valve with a flat, longitudinally finely striated ligament
surface just below the dorsal margin of each valve. Below the
flat surface on the anterior auricle is a narrow linear socket
followed by a long, strong cardinal crus. Posterior ear similar,
with a cuneiform-shaped depression defined ventrally by a cardinal
crus which is strongest near the resilifer and at its posterior end,
and which extends postero-ventrally and then bends up sharply to
meet the end of the flat surface. Right valve with a strong cardinal
crus on each auricle. These fit into matching depressions above
the crura of the left valve. The presence of flat ligament surfaces
on the right valve is uncertain, but probable, judging from the
photograph (pl. 6, fig. 4). Base of each auricle has a nodular
auricular crura, with the posterior being the stronger. Resilifer
small, with on the left valve two shallow depressions on either side.
These suggest the presence of short, weak tooth-like processes on
either side of the resilifer of the right valve.
Musculation and shell structure unknown.
DISCUSSION. Both left valves are similar except for stronger car-
dinal crura and more distinct radial ornament on the umbone of
USNM 62263.
24 Postilla YALE PEABODY MUSEUM No. 110
COMPARISONS. Pectinella sigsbeei is externally similar to Syncyclo-
nema halli. The main differences are in the details of ornament,
the strong inflation of the valves, and the very small posterior
auricle of P. sigsbeei. Both species have similar concentric
lamellae on the auricles, but the radial ornament of S. halli
is much stronger than that of P. sigsbeei and its concentric striae
are not so regular or distinctive. Consequently, S. halli does not
have the pseudopunctate effect of P. sigsbeei. S. halli lacks
the strong auricular crura of P. sigsbeei, and has strong tooth-like
processes on either side of the resilifer against possibly only weak
ones on P. sigsbeei. The auricles of the left valve of P. sigsbeei
have dorsal flat ligament bearing areas which are lacking on
S. halli. The cardinal crus on the posterior auricle of the left valve
of P. sigsbeei is arcuate and concave upwards (pl. 6, fig. 6), that
of S. halli is straight (pl. 3, fig. 1). The cardinal crus on the ante-
rior auricle of the left valve of P. sigsbeei is long and strong (pl.
6, fig. 5) whereas that of S. halli is weaker, sometimes discon-
tinuous, though relatively strong close to the resilifer and _ its
anterior end where the swollen part is displaced dorsally relative
topthe rest of (the crus (pli 3. fies; >).
These morphological differences are sufficient to warrant
accepting Syncyclonema and Pectinella as distinct genera. A
knowledge of the musculation might give additional support to
my conclusion.
Hayami (1965, p. 318) reclassified a Japanese Lower Cre-
taceous species, Pecten miyakoensis Nagao, under Pectinella.
Study of casts of P. miyakoensis (NZGS-WM 8473) shows that
externally the species resembles both S. halli and P. sigsbeei.
But the strongly projecting dorsal extremities of the auricles of
the right valve of P. miyakoensis are not matched by either species.
P. miyakoensis more closely resembles S. alli in the strength and
form of the radial and concentric ornament and lack of a pseudo-
punctate effect. As recognized by Hayami the ornament of P.
miyakoensis tends to be discrepant with stronger concentrics on
the right valve and stronger radials on the left valve. Also the
ornament of P. miyakoensis is markedly finer, and the radial
ornament more restricted to the dorsal flanks of the disc.
P. miyakoensis, like S. halli, lacks auricular crura. Contrary
to Hayami’s (1965) description, a right valve of P. miyakoensis
1967 REVISION OF SYNCYCLONEMA 25
has cardinal crura. (These are faintly visible on pl. 45, fig. 6,
of Hayami, 1965, Gk H6622). On either side of the sunken
resilifer, flat longitudinally striaed surfaces pass laterally into
narrow crura which extend halfway to the extremities of the
auricles. Small rounded protuberances extend ventrally from the
triangular surfaces on either side of the resilifer. The form and
arrangement of the crura and the strongly projecting auricles of
the right valve distinguish P. miyakoensis from both Syncyclonema
and Pectinella, and the lack of tooth-like processes on either side
of the resilifer distinguishes it from Syncyclonema.
Future studies on small, relatively smooth pectinids may war-
rant placement of P. miyakoensis in a separate supra-specific
taxon. Until adequate studies are completed, it is best to treat
it as a Pecten (sensu lato). Except for the large byssal auricle
and notch P. miyakoensis superficially resembles species of Ento-
lium by its possession of strongly projecting dorsal margins and
short cardinal crura.
5. GENUS HYALOPECTEN
AUTHOR. Verrill, 1897, p. 71.
TYPE SPECIES. By original designation, Pecten undatus Verrill &
Smith, in Verrill, 1885, p. 444, pl. 44, fig. 21 (= Hyalopecten
dilectus Verrill & Bush, in Verrill, 1897, p. 80, pl. 18, fig. 5; see
North, 1951), North-west Atlantic Ocean, Recent.
DISCUSSION. To document the differences between Syncyclonema
and Hyalopecten the poorly known type species of the latter is
redescribed from its holotype.
Grau (1959) classes Hyalopecten as a subgenus of Cyclopecten
Verrill (1897).
Hyalopecten dilectus Verrill & Bush
(CELSO. tiess<S, 92. ply Je tigss de 2)
Pecten undatus Verrill & Smith, in Verrill, 1885, p. 444, pl. 44,
fig. 21 (not Pecten undatus Defrance, 1825, p. 257).
Hyalopecten dilectus Verrill & Bush, in Verrill, 1897, p. 80, pl.
Salo. Se
For a full synonymy refer to North, 1951, p. 234.
26 Postilla YALE PEABODY MUSEUM No. 110
TYPE SPECIMEN. Holotype of H. dilectus Verrill & Bush, by
original designation, USNM 44827, Station 229, Albatross Expe-
dition, 1423 fathoms, off Maryland, Recent.
Holotypes have been proposed for both Pecten undatus and
Hyalopecten dilectus. | agree with both Dall (1898, p. 754) and
North (1951) in considering that P. undatus Verrill & Smith
and H. dilectus are conspecific. Consequently, under the Rules of
Zoological Nomenclature, Article 72d (Stoll, et al., 1961, p. 75)
the holotype selected by Verrill & Smith for their P. undatus
is valid.
REVISED DESCRIPTION. Shell very thin, equivalve, although umbone
of left valve projects above dorsal margin and is more inflated
than that of right valve, subequilateral. Measurements: length
18.8 mm, height 20.0 mm, half width 3.0 mm, length of ante-
rior ear from umbone to extremity 5.6 mm, length of dorsal
margin 11.0 mm. Dorsal margin of ears does not project above
ligament attachment area. Both valves have distinctive ornament
of fine radial plicae, subdued on inner shell surface, and con-
centric growth striae and regular broad plicae. Radial plicae much
finer and weaker on the dorsal flanks, consisting of 155 and 140
on the left and right valves respectively. Secondary radial plicae
appear by intercalation on upper third of shell, and tertiaries
close to ventral margin. Concentric plicae number 17 on left and
14 on right valve. Protoconch of both valves smooth. Auricles
small, of approximately equal size, extremity of posterior auricle
pointed, and all except byssal auricle of right valve are not
demarcated from main disc of shell. Byssal auricle of right valve
overhung by margin of main disc of shell, outermost margin of
which projects upwards as a thin flange. Strong ctenolium is
hidden under overlapping margin. Byssal auricle with wide fas-
ciole covering half of its surface, fasciole ornamented by con-
centric growth costae, and dorsal half of auricle with five radial
costae. Byssal notch deep, narrow, V-shaped. Hinge weak; each
auricle with narrow, flat-topped crus (for ligament attachment?)
followed below by shallow linear depression and very weak
cardinal crus, latter being barely evident on posterior ear.
Resilifer very small and shallow, that on right valve bordered on
anterior side by very short and weak tooth-like ridge (? abnormal
1967 REVISION OF SYNCYCLONEMA DY
asymmetry). No auricular crura. Muscle scars not impressed,
unknown. Shell of two layers of unknown structure; translucent
outer layer and thin white inner layer covering dorsal third of shell.
COMPARISON WITH SYNCYCLONEMA. The strongly plicate
valves with numerous fine radial costae differ markedly from the
virtually smooth non-plicate valves of S. halli. H. dilectus has
small pointed auricles whereas those of S. halli are relatively larger
and their extremities rounded. A ctenolium is present on H. dilectus
but lacking on S. halli, and the cardinal crura on H. dilectus are
exceptionally weak compared to those of S. halli.
PSEUDAMUSSIUM
The status of Pseudamussium has been controversial. Soot-
Ryen (1962, p. 254) correctly points out that the name has been
used for two “quite different groups of pectinids”; (1) Pseuda-
mussium Morch (1853) with Pecten septemradiatus Miiller (1776)
as type species, and (2) Pseudamussium H. & A. Adams (1858)
with Ostrea hybrida Gmelin (1791; = Pecten exoticus Chemnitz,
1784) as type species (Grau, 1959). The correct application of
the name depends on the validity for nomenclatural purposes of
Morch’s catalogue. The International Commission of Zoological
Nomenclature, Opinion 714 (1964) has validated under the
Plenary Powers Pseudamussium Moé6rch, 1853, with Pecten
septemradiatus Miller (1776) as type species.
6. GENUS PSEUDAMUSSIUM Morch
AUTHOR. Morch, 1853, pt. 2, p. 59.
TYPE SPECIES. By designation under the Plenary Powers, Pecten
septemradiatus Miller (1776, p. 248), Eastern Atlantic Ocean,
Recent.
Pseudamussium septemradiatum (Miller)
Pecten septemradiatus Miiller, 1776, p. 248.
Pseudamussium septemradiatum (Miiller). Morch, 1853, p. 59.
Soot-Ryan, 1962, p. 225.
28 Postilla YALE PEABODY MUSEUM No. 110
SYNONYMY. See Grau (1959) and North (1951) for discussions
of this species. No restatement of its full synonymy can be
attempted here.
TYPE SPECIMENS. Now that the type species has been designated
a type specimen should be selected by a worker familiar with the
species, preferably from the collections studied by Miller (1776).
DESCRIPTION. “Pectens” of the septemradiatum group, sometimes
synonymized with Peplum Bucquoy, Dautzenberg & Dollfus (1889;
Grau, 1959), have strong radial plicae, relatively small ears, with,
fasciculatum (Hinds, 1845), or without, septemradiatum, a cteno-
lium on adult specimens, a shallow open byssal notch, the auricles
are delimited from the disc of the shell, and the byssal auricle of
the right valve lacks a definite fasciole and has strong radial
costae. The following hinge and musculation details are based
on specimens (NZGS-WM 2778) of Pseudamussium septem-
radiatum (Miller).
Right valve has on each side of resilifer a short, transversely
striated surface (provinculum) which extends one quarter of
distance towards extremity of ear. Commencing above end of these
surfaces and continuing to end of ears is a weak cardinal crus
possessing a transversely striated upper surface. The short surfaces
(provincula) fit into matching concave striated depressions on
either side of resilifer of left valve and the cardinal crura into
relatively deep depressions situated above weak cardinal crura
which extend from ends of the provincula sockets. No tooth-like
processes bordering resilifer of right valve and no auricular crura.
Adductor impression subcircular, centrally constricted, sited above
mid-height close to base of posterior auricle, that of right valve
more so, and a series of very small impressions extends up to and
across end of umbonal cavity. Adjacent to anterior auricle are
two small circular impressions, one at antero-dorsal end of
umbonal cavity and one near ventral end of auricle. Pallial line
continuous.
COMPARISONS. See below under “Pseudamussium” hybridum.
“Pseudamussium” hybridum (Gmelin)
(PE, digs: 3-8)
1967 REVISION OF SYNCYCLONEMA 29
Ostrea hybrida Gmelin, 1791, p. 3318.
Pecten hybridus (Gmelin), Dall, 1898, p. 751.
For a detailed synonymy of this species see North (1951) and
Grau (1959).
TYPE SPECIMENS. When the supraspecific status of this species
has been clarified a type specimen should be selected, preferably
from the collections available to Gmelin (1791).
TABLE 1: Measurements of seven valves of Pecten hybridus Gmelin
held in USNM 131671. All measurements in millimeters.
Length
Half Anterior Dorsal HAM
Valve Length Height Width Length Margin =
right Dir 20.4 2.4 6.6 NSE 9.0
4 20.2 19.9 2.8 Soll ES. 9.2
left 2353 23.4 4.1 5) 11.0 10.1
© 23.0 235) 3.6 4.3 9.1 11.6
17.0 16.7 of) 38) Tes 7.6
1 Se2 IS o9/ py) 3.8 7.8 —
13.0 DED D3 Beil 7.4 —
* HAM — height of base of adductor muscle impression above the ventral
margin.
REVISED DESCRIPTION. A redescription of the characteristic species
of the hybridus group of Pectinids, Ostrea hybrida, based on the
collection (USNM 131671) studied by Dall (1898, p. 751),
follows:
Small, length of specimens (n = 7) 13 to 23.3 mm, dimensions
as given in Table 1, equivalve, subequilateral, although umbone
of left valve is more inflated and projects slightly above margin
of commissure. Left valve with 62 to 87 round-topped radial
costae, including rare intercalated secondary costae. Radial costae
wider than interspaces. Costae weaker on ventral half of shell,
and are worn on available specimens. Valve also ornamented by
irregular growth depressions and fine regular growth striae which
produce nodes where they cross radial costae and lamellar projec-
tions across interspaces. Ornament strongest on juvenile speci-
30 Postilla YALE PEABODY MUSEUM No. 110
mens. Right valve has concentric growth depressions, striae, and
radial costae only on dorsal flanks of disc and on auricles.
Auricles subequal, posterior slightly longer than anterior. Posterior
auricles and anterior auricle of right valve not delimited from shell,
with four to seven radial costae. Byssal auricle of right valve has
a narrow deeply impressed fasciole, and on area above, five to
six strong radial costae which become more widely spaced
ventrally. Byssal notch narrow, deep U-shaped, bordered ven-
trally by ctenolium of 19 to 21 nodules.
Each auricle of right valve hinge has one dorsal crus which
thickens outwards, is flat-topped with fine transverse striae, fol-
lowed below on the inner half of auricle by a deep narrow socket
and an underlying, raised surface (provinculum) with coarse
transverse striae which merges with the dorsal crus at end of socket.
Very weak and short tooth-like ridges occur on each side of resili-
fer. Each auricle of left valve has a relatively strong dorsal crus
with a transversely striated upper surface, below which on inner
half of ear is a concave striated surface for reception of matching
raised surface (provinculum) of right valve.
Adductor muscle impression, situated posterior of center at
about mid-height, consists of two overlapping suboval portions
(quick and catch muscle impressions), with two discrete small
oval impressions antero-dorsally above. Two small oval impres-
sions occur in umbonal cavity adjacent to base of anterior auricle,
one at top of umbonal cavity, the other close to byssal notch.
Pallial line continuous. Central third of inner shell surface, on
outer shell layer, marked by fine radial striae.
COMPARISONS. “Pseudamussium” hybridum and P. septemradiatum
differ primarily in external morphology. The former has weak
ornament which is discrepant, with the left valve possessing fine
radial costae or striae and the right valve being smooth or having
weak radial ornament which is best developed on the dorsal flanks
of the shell, a narrow fasciole, and a strong ctenolium. P. septem-
radiatum has similar plicate ornament on both valves, and no
fasciole or ctenolium. The pattern of muscle impressions and the
hinge morphology of both species are similar, except that “P.”
hybridum has weak tooth-like processes at the end of the pro-
vincula on either side of the resilifer and its cardinal crura begin
1967 REVISION OF SYNCYCLONEMA Sil
above the outer end of the provincula and not near the resilifer
as on P. septemradiatum.
These differences, especially of ornament, if consistent over
the species included in the groups, possibly warrant separation
at the subgeneric level of the “P.” hybridum group from the
P. septemradiatum group.
Syncyclonema differs in external and internal morphology
from both Pseudamussium septemradiatum and “P.” hybridum
groups. The radial plicae of P. septemradiatum and the radial
costae and discrepant ornament of “P.” hybridum are in no way
similar to the virtually smooth shell of S. halli. Provincula sur-
faces and dorsal flat-topped cardinal crura are present on P. sep-
temradiatum and “P.” hybridum but absent on S. halli. The cardi-
nal crus on the posterior ear of the left valve of P. septemradiatum
and “P.”’ hybridum are long but are short on S. halli. P. septem-
radiatum and “P.” hybridum have a subcentral muscle impression
but that of S. halli is close to the base of the posterior ear.
GENERAL COMMENTS
Further detailed morphological and nomenclatural studies are
required to clarify the generic status and the phylogeny of small
pectinids. Data from musculation, hinge morphology, and _ shell
structure, may facilitate classification. Hinge morphology and its
terminology warrants close attention. The distinction of cardinal
crura which bear ligament attachment areas from those that do
not may help classification.
Syncyclonema differs from the genera it has been compared to
in the past by external or internal morphology, or both. Lack of
knowledge of the morphology and biostratigraphy of small Upper
Cretaceous and Lower Tertiary pectinids prevents a discussion
of the phylogeny of Syncyclonema. The occurrence of externally
closely similar species in the Cretaceous (Pecten miyakoensis),
Eocene (Eburneopecten scintillatus), and Recent (Pectinella sigs-
beei) suggests the widespread occurrence of homeomorphy in
the Pectinidae.
By, Postilla YALE PEABODY MUSEUM No. 110
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1967 REVISION OF SYNCYCLONEMA 35
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